Onset of Labour

Labour and delivery normally occur between 37 and 42 weeks gestation.

There are three stages of labour:

  • First stage – from the onset of labour (true contractions) until 10cm cervical dilatation
  • Second stage – from 10cm cervical dilatation until delivery of the baby
  • Third stage – from delivery of the baby until delivery of the placenta

 

First Stage

The first stage of labour is from the onset of labour (true contractions) until the cervix is fully dilated to 10cm. It involves cervical dilation (opening up) and effacement (getting thinner). The “show” refers to the mucus plug in the cervix, which prevents bacteria from entering the uterus during pregnancy, falling out and creating space for the baby to pass through.

The first stage has three phases:

  • Latent phase – from 0 to 3cm dilation of the cervix. This progresses at around 0.5cm per hour. There are irregular contractions.
  • Active phase – from 3cm to 7cm dilation of the cervix. This progresses at around 1cm per hour, and there are regular contractions.
  • Transition phase – from 7cm to 10cm dilation of the cervix. This progresses at around 1cm per hour, and there are strong and regular contractions.

 

Braxton-Hicks Contractions

Braxton-Hicks contractions are occasional irregular contractions of the uterus. They are usually felt during the second and third trimester. Women can experience temporary and irregular tightening or mild cramping in the abdomen. These are not true contractions, and they do not indicate the onset of labour. They do not progress or become regular. Staying hydrated and relaxing can help reduce Braxton-Hicks contractions.

 

Diagnosing the Onset of Labour

The signs of labour are:

  • Show (mucus plug from the cervix)
  • Rupture of membranes
  • Regular, painful contractions
  • Dilating cervix on examination

 

NICE guidelines on intrapartum care (2017) refer to the latent first stage and established list stage.

The latent first stage is when there are both:

  • Painful contractions
  • Changes to the cervix, with effacement and dilation up to 4cm

 

The established first stage of labour is when there are both:

  • Regular, painful contractions
  • Dilatation of the cervix from 4cm onwards

 

Last updated September 2020
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